Tuned transmission circuits



w. D. LOUG HLIN TUNED TRANSMISSION 'cmcuI T's 6 Sheets-Sheet 1.

Filed dec. 22, 1931 May 7, 1940. w. D. LOUGHLIN TUNED TRANSMISSIONCIRCUITS e Sheets-Shet 2 Filed Dec. 22. 1931 i VIII/l IIIIZ May 7, 1940-w. '0. LOUGHLIN TUNED TRANSMISSION CIRCUITS Filed Dec. 22, 1931 eSheets-Sheet b' y' 1940! w. D. LOUGHLIN 2,199,669

TUNED TRANSMISSION CIRCUITS I Filed Dec. 22, 1951 a Sheets-Sheet 4 W. D.LOUGHLIN TUNED TRANSMISSION CIRCUITS May 7, 1940.

6.Sheets-Sheet 5 Filed. Dec. 22, 1951 Illllll/ lllllllll: V

l h J y 7, 1940- w. b. LOUGHLIN 2.199.669

TUNED TRANSMISSION CIRCUITS Filed Dec. 22, 1951 6 Sheets-Sheet 6Patented May 7, 1940 UNITED STATE TUNED TRANSMISSION CIRCUITS William D.Loughlin, Mountain Lakes, N. 1., assignor, by mesne assignments, toRadio Corporation of America, New York, N. Y., a corporation oi.Delaware 1 Application December 22, 1931, Serial No. 582,632

7 Claims. (Cl. 250-40) s PATENT OFFICE This invention relates to tunedtransmission circuits and more particularly to circuits of the type inwhich the resonant frequency is determined by adjustment of theposition, in the magnetic field of an inductive element of the circuit,of an armature that has a permeability greater than unity foralternating magnetic fields.

Circuits of this type are commonly known as iron-tuned circuits and, asa matter of convenience, that term will be employed in the followingspecification and claims but it is to be understood that tuning armaturemay includ a metal or alloy other than iron.

The mechanical construction previously employed for iron-tuned circuitshave included fixed tuning armatures and movable coils. Individual tunedcircuits exhibit desirable electrical characteristics but considerabledifficulty has been ex perienced in alining a plurality of circuits thatare to be tuned simultaneously by an adjustment of the coils withrespect to stationary armatures.

An object of the invention is to provide an improved mechanicalconstruction for a tuning system of the type including magneticarmatures or cores. A further object is to provide a tuning system ofthe type stated in which the tuning armatures are mounted on a movablecarriage, the carriage being adequately supported and guided forsubstantially rectilinear movement. Further objects relate to theprovision of jigs for the accurate mounting of a plurality of inductancecoils in substantially parallel and/or coaxial relation. Further objectsrelate to the provision of improved electrical circuits for use withresonant circuits ofthe iron-tuned type and to methods of alininglsuchresonant circuits for gang tuning.

These and other objects of the invention will be apparent from thefollowing specification, when taken with the accompanying drawings, in

which,

Fig. l is a plan view of one embodiment of the invention,

Fig. 2 is a fragmentary horizontal section through one tuning unit ofthe multi-stage tuner shown in Fig. 1,

Figs. 3 and 4 are vertical sections on line 11-41 of Fig. 2, as viewedin the directions indicated by arrows 3-3 and 4-4, respectively,

Fig. 5 is 'an expanded perspective view of a double condenser unit,

Fig. 6 is a perspective view of the mounting plate which supports thedouble condenser and the coil assembly,

. Fig. '7 is a central section through a coil form mounted on a mountingjig,

Fig. 7a illustrates a modified mounting for the coil,

Fig. 8 is-a similar central section through the mounting plate,

Figs. 9 and 10 are a side and a plan view, respectively, of anotherembodiment of the invention,

Fig. 11 is a perspective view of another form .of multiple unitassembly,

Figs. 12 and 13 are side and end views of another multiple unitassembly,

Fig. 14 is a vertical section on line 14-44 of Fig. 13,

Fig. 15 is a fragmentary central section of a coil form and mount, astaken on line l5l5 of Fig. 17,

Figs. 16 and 17 are top and bottom views, respectively, of a coil formand mount, and

Figs. 18 and 19 are fragmentary circuit diagrams of a radio receiverincluding a plurality of iron-tuned circuits.

In the four unit assembly illustrated in Figs. 1 to 8, inclusive, thenumeral l identifies a rectangular frame which may be, and preferablyis, formed of a relatively heavy steel plate. A steel strap 2 is securedacross the frame, and two of the coil assemblies are secured to thestrap and twoare secured to an end bar of the frame. The

. coil assemblies are arranged in two longitudinally alined sets, andthe tuning elements 3 are similarly alined and adjustably secured, byset screws 4, to a pair of brass rods 5 which extend beyond each end'ofthe frame I. At one end, the rods 5 are rigidly secured to a yoke 6 intowhich the adjusting screw I is threaded. The adjusting screw isrotatably supported, and without end play, between a ball bearing 8 thatseats in a depression in the frame I, and a strap 9 that is fixed to theframe. The outer end of screw 1 is provided with an appropriateoperating means, such as a tuning knob Ill.

As shown in Fig. 2, each moving element comprises a cylindrical bodyhaving a deep annular counterbore ii providing a core and sleeve. Fortuning to radio and intermediate frequencies, these tuning elements maycomprise masses of finely divided iron which are accurately molded tothe desired form by a binder that'has the additional function ofinsulating the particles of iron from each other.- The counterbore llpermits the coil form l2, with its winding or windticns of the tuningelement 3.

The rods I pass loosely through the end bars of frame I but areaccurately guided in bearing openings in the plates l4 secured tocorresponding faces of the end straps of frame I and thecrow strap 2. I

For convenience of manufacture, all of the plates I4 may be of identicalform, being angle plates as shown in perspective in Fig. 6. The twoplates It at the end of the frame opposite the adjusting screw I are"dummy" plates, while the remaining plates "l4 carry the coil form l2 ofthe several units. In addition to the bearing apertures I5, eachmounting plate I is provided with threaded openings it for receiving thescrews ii that secure the plates to the frame I and strap 2. By means ofgang punches, the openings l5 ii are accurately located in the platesII. The plates H are also provided with openings I! for receiving thebolts l9 that are used to attach the coil forms i2 to the mountingplates. As shown in Fig. 7, each coil form 12 is accurately mounted onits plate I! by means of a jig 20 that comprises a cylinder which has asnug fit within the coil form, and a cylindrical projection 2i that fitssnugly within the bearing opening I! of the plate H. The method ofmounting the coil forms on the plates will be apparent from Figs. '7 and8 which, while separate views, indicate the relative position of theparts as the coil form is applied to its plate. The end face 22 of thejig 20 is accurately turned to a surface normal to the axis of theextension 2| and, when the Jig 20 is pressed firmly against the plate I,the axis of the coil form is normal to the surface of the plate is. Whenthis condition obtains, nuts are applied to bolts is to secure the coilform to the mounting plate. The coil forms are provided, as iscustomary, with soldering lugs 23 for completing the electrical circuitsto the windings on the form.

The angle or top flange of the plate 14 pro- 'vides a mounting for andconstitutes one electrode of a double condenser assembly which isarticularly useful in resonant circuits of the iron-tuned type. As shownin Fig. 5, this double condenser includes a bent strip 24 of copper orother metal having some resilience; insulating strips 25 of mics and asecond plate 26 being arranged between the sections of the strip 24. Asoldering lug is formed on plate 25, but a separate plate 21 bearing asoldering lug is preferably arranged above the.folded end of the bentstrip 24. The assembled condenser unit is illustrated in Fig. 4. A plate2| is arranged below and insulated from the flange of mounting plate I4,and screws are passed through the assembly toflex the lower fold of thestrip 24 towards the insulating strip 20 and the flange of plate I. Aheaded bolt 2. passes through the opposite ends of plates 24, 2|, beinginsulated therefrom, and enters a threaded opening in the flange. Turnindown of the bolt 30 flexes the free ends of plate 2| towards plate 2',thus increasing the capacity betweenthese plates.

The inductances on the several coil forms II are shielded from eachother'by aluminum or copper tubes II that have a length somewhat lessthan the maximum length of each' tuning unit. The free ends of the tubesare preferably provided with internal flanges 32 which 'may assist inguiding and supporting the relatively heavyiron timing elements 2. Attheir opposite ends, screws are riveted to the'tubu and,passingthroughthe eenterstrapI orthe endstrap amaeso of frame I, receivenuts 22 for securing the cans to the frame.

In adjusting the assembly to effect the simul-' taneous tuning of theseveral units to the same frequency, the adjusting knob II is firstturned to move-the armatures to the position shown in Figs. 1 and 2, i.-e., the armatures are moved to the position in which they exercise aminimum influence upon the inductance of the several coils .ortransformers. with ferro-magnetic armatures this willbe the position ofmaximum frequency, i. e., the high frequency end of the tuning range.The several shunt capacities are then adjusted, by means of the bolts30, to bring all units into resonance at the wave length lower limit ofthe frequency band. The inductances I! or coil forms l2 serve as themeasure for determining the magnitude of the several shunt capacitieswhich constitute the fixed elements of the tuning units; thusdistinguishing from the prior practice with respect to capacitivelytuned circuits in which the fixed elements, i. e., the inductances, arecarefully equalized before any attempt is made to adjust the variableelement 0: tuning capacities of the units. Having adinstead thecapacities to aline the units at the wave length lower limit of the bandof frequencies, the knob I0 is manipulated to bring the armatures withinthe coils and the several armatures are then adjusted longitudinally ofthe supporting carriage to bring all units into resonance at onefrequency. All units are then exactly syntonized at two differentpositions of the tuning control, and in general, will be substantiallyin resonance with each other throughout the entire tuning range.

It is obvious that this'p'rocess of adjustment in general producesperfect syntonism betweenthe, several tuned-circuits at all positions ofthe armature provided that the following two conditions are fulfilled:(l) the initial inductancw of the coils are equal with the armatures allthe way out of the field; (2) the physical arrangement of the system issuch that the rate of change of inductance with displacement of themagnetic armature is the same for each unit.

In practice it may be desirable to preserve tuning alignment withinductances which are not precisely equal at the high frequency end, orconversely to preserve alignment with an armature system wherein theinductance of one unit varies more rapidly than the inductance ofanother. The electrical requirement for tuning alignment is that theproducts of the inductances of all the coils by the capacities of theirrespective shunt condensers shall be equal at each position of thetuning control. Suppose one coil has a larger initial inductance thananother. At the high frequency end of the band the fixed tuningcapacities connected across these coils will be. adjusted to the sameratio, inversely to each other as the inductances of their respectivecoils. Then to preserve tuning alignment over the band, it will benecessary for this initial ratio between the coil inductances to bepreserved at all positions of the armature. In other words, if oneinductance is 1.05 times as large as another at the high frequency end,the functional relation between inductance and position of the tuningcontrol must be so chosen or adjusted that the first inductance varies1.05 times as fast as the second throughout the tuning range. Thetuning'system described above is designed to facilitate sucharrangements. For example, I may predetermine the rate of change of in-30 I are secured to the cross straps and to one end ductance withposition of the tuning control by the use of term-magnetic armatureshaving different values of permeability for different units of the sameassembly. Or I may, by adjusting the mounting screw, vary the angleswhich the coil forms l2 make with the direction of travel of the tuningarmatures as shown in Fig. 7a.

In said last-mentioned figure, the mounting screws l9 are providedwith'springs S, S respectively, which are interposed between plate l4and the screw-heads. The holes l8 in the arrangement shown in Fig. 7aare threaded so as to provide for adjusting the screws I9. It isbelieved to be obvious from a study of the drawings that the angle whichthe coil form I2 makes with the direction of travel of its tuningarmature may be adjusted by simply screwing down one of the screws l9more than the other.

Where but three tuned circuits are required, the assembly shown'in Figs.9 and 10 may be employed to advantage. The construction of theindividual units may be, and preferably is substantially identical withthat previously described. In place of an open frame, the several unitsare mounted in a chassis 34 having the form of a steel box open at thebottom, and having flanges 35 for securing the box to the main chassis'of the receiver. Cross straps 2 extend across the box frame 34, and themounting plates l4 of the box, the flanged ends of the several platesbeing at the open bottom of the box to permit access to the condenseradjusting bolts through openings in the chassis plate to which the boxframe 34 is secured.

The carriage rod 5 is, as previously described, slidably mounted in theseveral mounting plates and ma dummy plate l4 at the exterior of box 34.The opposite end of the rod 5 has an L- shaped strap 36 rigidlysecuredthereto, and an accurately cut rack 31 is formed on or secured to thestrap 36. The rack 31 is engaged by a pinion 38 on shaft 39 that isjournaled in bracket 40 and carries an adjusting knob 4!. The free endof strap 36 passes through a slot in an angle bracket 42, and anadjustable guide plate 43 on bracket 42 extends across one end of theslot in the bracket. A leaf spring 44 onbracket 42 presses the strap 36into engagement with the guide plate'43, and, by suitable adjustment ofthe plate, the rod 5 is guided for straight line motion.

In place of the described tandem arrangement of the several tuningunits, a parallel arrangement may be employed when due precaution istaken to prevent inadvertent yawing of the several iron elements. Asshown in Fig. 11,'the frame 45 for supporting the coil assemblies andthe mounting plates (as previously described) for guiding rods 5 has theform of an open sided box.

The several rods 5 are parallel to each other and have their outer endsthreaded into a cross bar 46 which has flanged ends 41 extending alongthe ends of-the box frame 45 and guided in slots in brackets 48. The endflanges 41 of the cross bar 46 are provided with racks 49 that areengaged by pinions 50 on" a sturdy shaft 5| that is journaled in flanges'48 and carries an operating device, aslndicated by knob 52.Leaf-springs 53 are'secured to bosses on brackets 48 to hold the racks49 inclose engagement with the pinions so. 4,

As shown in Figs. 12 to 14, a different style of carriage for mountingthe several iron tunnumber of tuned circuits are required, but may, ofcourse, be used with either more or less tha the six units which areillustrated. 1

The mountingand general shield for the sev-' eral units comprises arelatively heavy steel box 54 having a cover plate 55 secured thereto.The end wall and cover plate of the box are apertured to receive andaccurately guide the rods 56 to which the supporting plate 51 is rigidlysecured. The supporting plate is accurately bored and threaded to.receive the bolts 58 to which the iron tuning units 3 are secured. Theend wall of box 54 is apertured to permit access to the kerfed ends ofthebolts 58 to permit adjustment thereof with respect to supportingplate 51 for alinement of the several units.

The sliding carriage formed by plate 5'! and rods 56 may be operated inany suitable manner and, as illustrated, the operating mechanism issubstantially as shown in Fig. 1. The ends of rods 56 are joined by ayoke 59 that is threaded to receive an operating screw 68 that ismounted in a strap 6| and carries a knob or other operating device 68'.

The coil assembly may be of the type previously described or, asillustrated, the coil forms 62 may have end plugs 63 which receivescrews 64 securing the same to the circular and flanged mounting caps65. Witnin the flange is mounted a condenser comprising plates 66, 61,which are insulated from each other and from the mounting cap by mica68. A bolt 69 extends through cap 65 and carries an adjusting nut 10which is accessible through openings II in the box cover plate 55 whenthe cap is secured thereto by screws 12. The tubular shields" 13 foreach coil unit have'a frictional fit with the flanges of the mountingcaps 65. An arcuate portion of the mounting cap 65 is cut away, and aninsulating plate 14, carrying terminals 15, is secured over the cut-outportion. I

Preferred types of electrical circuit arrangements for iron-tuned unitsare shown in Figs. 18 and 19.

The illustrated radio receiver includes two carrier wave amplifier tubes80 and a detector tube 8|, and the couplings to and between the tubescomprise iron-tuned transformers which are units of a gang .assembly,such as one of those described above. The transformer windings are ofrelatively fine wire, wound turn for turn on the coil forms andconnected in the same sense, thus providing a substantiallyunitycoupling between the primary P and secondary S.

It will be noted that the primary winding P of transformer T of theinput stage is connected between ground and the control grid, thecollector system being also .connected to the grid. The condenser C isconnected across the secondary S, and the low potential (carrierfrequency) terminal of thesecondary is connected to the tube cathodeand, through a condenser C, to ground.

The plate circuits of the carrier wave amplifiers include the primarywindings P of the transformers T and T respectively. The secondarywindings S are shunted by relatively fixed condensers C, the terminalsof the winding S of the transformer 'I being connected to ground and,through a coupling condenser Cc, to the high potential terminal of thecorresponding winding S of the input transformer T of the second car- 75an'inductance, the inductance of one circuit being unequal to theinductance of another cir-' cuit, and addustable means forsimultaneously varying the inductances of all of said circuits over afrequency band, said tuning meansmaintaining a constant ratio betweensaid unequal inductances throughout the tuning range .01 said circuits.1

7.1natransniission system,apmrality ot o tuned circuits each comprisinga fixed capacityancace c W 5 means for adjusting th'rate oi change ofinductance for each coil.

mun. LOUGHLIN. m

